Extensometer



prifi 29, 1937.

G. S. VON HEYDEKAMPF EXTENSOMETER Filed Jan. 14 1933 Patented Apr. 20, 1937 umfl-zo STATES PATENT OFFICE 2JW'L598 EXTENSOME'IER.

Gerd S, von Heydekampt, Oheder, Pa. 'asslgnor to Balalwln-Southwarl: Corporatlon, a corporatlon ot Delaware 'Ihis 1nventlon relates geherally to extensometers end more particularly to an lmproved extensometer adapted to remaln attached to a. speclmen durlng Iailure thereot without lnjury to the extensometer.

In the use of usual forma of extensometers lt 1s necessary to remove the same Irom a. speolmen betore; lts breaklng polnt ls reached to prevent lndury to the extensometer, th1s belng partlcularly true o! cast Iran or other brlttle material where fallure occurs suddenly. Hence wlth these arrangements lt ls lmposslble to obta .ln completestress-straln data rlght up to the polnt of iallure.

It ls one object of my lnventlon to provlde an lmproved extensometer adapted to permlt straln readlngs through the polnt of fallure end partlcularly to allow the Instrument to remain attaohed to a speclmen durlng fallure thereof wlthout injury to the extensometer; A further object 1s to provlde an lmproved extensometer frame' having a plurallty of separable er relative movable parts adapted to be bald in normal operative fixed relatlon to each other and to a speclmen durlng normal testing but upon fallure of the specimen seid plurallty of parts will functlon to avold indury to the extensometer frame or any cf lts parts.

Another object ls to have an extensometer of the the foregolng typ8, Particularly a straln averaglng extensometer, provided wlth improved means whereby the extensometer may be attaohed to specimens 017 dlfierent diameters or slzes without afiecting the accuracy of the readings or the averaglng characterlstics thereof. In the specific aspect o f thls phase of the inventlon I have provicled an lrlzgensometer havlng grlpplng heads axlally ofl.set from the body or yleldable portlon of the maln frame whereby a palr 01 opposed adjustable gauge contacts are adapted in an improved manner to render the extensometer accurately available Ior speclmens of ditlerent diameter. In general, to accompllsh the various objects I have provlded a normally breakable trenne comprlslng a maln frame havlng a gr1p- 5 plus head; end a normally separable gripping head engaglng a dummy or platform head formed a.s part of the maln Irame. A further object 1a to provlde lmproved means for centering the separable gripplng hea.d end also to malntaln the head substantlally normal to the speclmen axls. I also preferably employ yleldable means Ior holdlng the separable parts of the extensometer together whlle lt is attached 1:0 an unbroken specimen. Another object is to have an extensometer of the type herein dlsclosedprovlded with lmproved strain averaglng means und mldrometer adjusted electrical contacts adapted to be connected to any sultable recording mechanlsm wlth means for automatlcally adjusting the contacts durlng strain o1 the speolmen. 1 5

' Other objects anal advantages will be more apparent from the following description 015 the ac companying dra.wlng in whlch:

Flg. 1 ls a perspective of my improved extensometer applied to a speclmen which 1s only 10 partlallyshown;

.Fig. 2 ls a side elevation of the extensometer taken on a vertical plane substantlally on the llne 2-'-2 of Fig. 1;

Flg. 3 is a horizontal sectlon taken substantlally 15 on the line 33of Flg. 2

' Fig. 4 ls a side elevation of the extensometer as lt appears after the sDecimen has failed, parts of the extensometer fram.e being shown in sectlon along the line 4-4 of Fig. 3; 2

Fig. 5 is a plan vlew of the normally separable grlpplng head.

Figure 6 is a slde elevatlon of the straln averag ing means, parts being broken away.

One form which the invention may take among 25 posslble others, is shown herein as comprlslng a main frame havlng substantially parallel side legs l und 2 connected by an end leg 3 whlch 1s relieved as by opposed transverse grooves 4 and 5 to provide an axlally extending reduced por- 30 tion er web It will be noted' that these legs are formed of relatlvely wlde fiat material 02 narrow thiokness thereby provlding a high degree of rlgidity in the transverse dlrection together with sufilcient fiexlbility in the relleved portlon 35 015 the frame to permit relatively free axlal 1hovement during strain of the-speclmen. The sldes l and 2 and end 3 may be formed from a slngle integral member although it is preferable that these component parts be formed separate'and 40 then welded, soldered or otherwlse sultably secured along abuttlng surfaces lndicated by the dotted llnes 6'.

The free end of side I has an axlally extending portlon 1 transversely ofiset from, or appreclably wider than the sldes l 'and 2 while a grlriping head geherally indicated at 8 projeots lateralljr from portlon l and is axially ofiset from side leg l, thus providing broadly an ofiset head in one or both of dlfl5erent dlrections. The other side 0 y leg 2has an axlalportlon 9 likewise wider than said side legs to carry an oflset dummy head or platform III. The head 8, portion l and. side leg I are preferably formed from a solld plece 01 metal suitably machlned to tlreshape shown al- 55 though lf deslied these coniponent parts may be Iormed separately and welded together along Dutt joints in the manner as shown by the llnes The same integral er separate constructlon may be employed for head I0, portion 9 und slde leg 2. The side legs I and 2 are relieved on each 61 thelr opposlte sldes as lndicated a.t II and I2 thereby to prov1de reduced horizontal "portlons or webs I3. Suita.blerelatlvely large recesses I4 and I5 are formed respectlvely in the heads 8 and I0, those recesses being of any suitable shape and of sufiiclezit size to recelve speclmens of cllfierent diameters or cross sections.

The heads 8 end I0 are prevented froxn havlng excessive axial movement away fromeach other due to the provlslon of preferably two stop rods IG and I1 extendlng through sultable allgned openings in each of sald heads and provided w1th enlarged portlons I8 recelvable in suitable recesses I9 to engage the bottoms thereof to llmlt movement of theheads. On the other band to obta.ln uniform ganze length of the extensometer whenever applied to a. speclmen spacing sleeves 20 und. 2I respectively surround rods I5 a.nd I1 so es to ahnt against the heads when the same .are pressed together .by the opera'tors flngers, lt being prefeiable that these sleeves are soldered er otherwise fixed to one of the heads such es I0. There ls also provided strain follow-up compresslon springe. 22 and 23 lnterposed between hea.ds I0 and 8 end. surroundlng guide rods 24 und. 25 which are preferably carried by one of the heads such for example as I0 in spaced relationto the other head. The gauge or spacer sleeves 20 am]. 2I are preferably dlsposed to one slde 01 the head as shown in Fig'. 3 whlle the follow-up springs 22 and 23 are disposed preferably in vertical allgnment with the gripplng polnts to be described presently.

The gripplng head 8 has opposed adjustable threaded gauge polnts 28 am]. 29 wlth the screw 29 disposed beneath the slde leg I 01 the main frame. The use of opposed adjustable points 1s found to be highly deslrable and ls definltely provided for by having the gripping head 8 oflset from the frame side I. As a result of thls 1mproved arrangement, speclmens of difierent diameters may be received centrally within recess I4 with proper engagement and adjustment o! each o! the gauge polnts.

If usual extensometer practice was followed, a. second sei: of gauge points would be carried by head I0 but lt ls seen that lf such an arrangement were employed down through failure of the specimen, as when under tenslon, then the breaking in half of the specimen would cause one sei; of gauge polnts to be carried by one of the broken halves of the specimen and the other sei; of polnts by the other half. with consequent excessive pull and injury to the frame. T0 overcome this very serlous objection and also to permlt stress-strain data. to be obtained down to the point of failure, I have provided a second set of points 30 and 3I carried by separable mea.ns

5 in the form of a snpplemental Irame or normally separable gripping head generally lndlcated at 32, this head belng of substantially U-shape wlth the gauge point in the form of screws 30 and 3I threaded in the sldes of the frame. The slde legs of the separable frame have sultable recesses cf conlcal or other desired shape to receive conlcal abutment points 33 and 34 whereby a. fixed relation may be efiected between the separable gripping head and main frame. A I ;hird screw 35 performlng what might be termed a levellng tunetlon ls adjustably threaded in the end 015 the separable head. 32 to engage the speclmen at 90 from the other gauge polnts end thus prevent downward swlnging of the separable frame about the axis of gauge polnt screws and 3I. 5

T0 Iacllitate centerlng 015 the separable head with respect to the speclmen, there ls provided a centerlng platze 30 havlrig a v-shaped notch or other sultable recess 31 engaglng the surface of the speclmen. Thls plate ls normally held in any 10 fixed adjusted posltlon by two screws 38 having threaded engagement wlth separable frame 32 and receivable In slots 39 01 the plate. A slmilar centering platze 35 ls adjustably held by screws 38' to the underside of gripping head 8, but 15 a. simple machlnlng operatlon 015 the grlpplng 25 l heads 8 and I0 althoughlf desired the heads end plates may be tormed from a slngle plece suitably machined to the form shown. A plvot plate 45 is held in spaeed relatlon to platze 42 as by a palr ot spacer sleeves 48 and screws 41 30 extendlng through plates 43 45 and sleeves 48 for threadedengagenlent wlth lower grlpping head 8. An averaglng pln 48, Journalled in plates 42 and 45, has its axls substantlally in the center of the grlpplng heads so as to normally interseot 35 the a.xis of a properly centered speclmen. A supporting arm 49 ls carrled by and projects upwardly from pin 48 so as to have engagement at lts upper end wlth a knlfe edge 50 of a hell crank lever 5I whlch ls preferably bent lnwardly a.t its 40 lower end as shown for purposes 01 obtainlng um restricted operatlon of the varl0us elements. Disposed in allgnment wlth.the knlfe edge, whlch extends in a horizontal direction, is an upper averaglng plvot 52 carried. by hell crank lever 45 5I for pivotal engagement with the I:op platze 43. The axls of thls averaglng polnt is substantlally in the center o1 upper head I0 for normal lntersecti'on with the axisof a properly centered speclmen. The knife edge 50 and pivot 52 are 50 held. in th elr respectlve bearings by a spring 53 whlch has one end connected to pln 44 und the other end to a pln 54 projectlng Irom arm 49.

The lower end of lever 5I carries an lnsulated electrlcal contact polnt 55 having a nut 56 to 55 whlch an electrical wlre may be connected for transmltting to any suitable recording mechan1sm the electrlcal impulses created by engagement between contact 55 and the adjustable stem or contact 51 o1 a micrometer generally 60 indlcated at 58.- This mlcrometer has a fixed housing 59 provided wlth a. flange 50 suitably rigldly secured to arm 49 end insulated therefrom. The usual mlcrometer rotatable harre] GI carrylng su1table graduations is adapted upon 65 rota.tlon 01 the micrometer head 62 to cause rotation and axlal adjustment of the micrometer stem 01' screw contact 51. The mlcrometer head may be elther manually adjusted or 11 the stressstraln recording mechanism ls of the automatlc type havlng suitable rotatable restorlng means, thls restorlng means may be connected by belt or. other sultable flexible means to a pulley 83 on head 82.

' 0peration.-My Improved extensometer ls ap- 75 plied to a. specimen by flrst, centering the speciman and head with centering plate 30' and then securlng the lower gauge points 20 and 20 to a speclmen, .e. g. 00, whereupon the upper head I0 4 5 is pressed downwardly against the compress'ion then brought into engagementywlth the speciman to hold the Instrument in its operative relation. -To prevent downward swinging movement of the separable head about the ganze points 30 and 3I levelling screw 30 engages the side of the specimen. The speoimen is now subjected to an v increasing load or stress with the result that elongation 01 the specimen' will permit the upper and lower sets 01 gauge points 30, 3I and 23, 29 to move axially away trom each other although the upper platform 015 dummy head I0 will have its abutting points 33 and 30 kept in engagement with the separable heacl 32 by virtue o! the strain follow-up springs 22 and 23 urging the head I0 upwardly. As the extensometer' expands, hell crank 5I will swing about knife edge 50 in a clockwise directlon so as to break engagement between electrical contacts 55 and 51. 'Ihe micrometer head is then either automatically or manually adjusted to reestablislyengagement between said electrical contacts to allow current to flow from the insulated point 55 and 51 to one or the other 01 binding posts 61 carried. by and insulated from 40 the side leg 2, the other binding post being cannected by flexible wire to the micrometer screw. When the specimen ultimately falls, the separable head 32 will remain with one part oif the broken specimen and the main extensometer frame will remain with the other part of'the speclmen, the separable head mexely separating from points 33 and 34 without any injury, shock er distortion o1! any Kind to the main frame. 'I'he maximum separation oi! the lieads 8 and I0 at the instant 01 failure is limited by rods IG and their heads I8.

In the event that the opposite sides of the specimen to which the opposed gaugepoints are attached should have unequal elongation such as might occur due to unequal loading Still there is or the elongation at the axis thereof. 'I'his average strain is accomplished due to the averaging pins 43 and 52 intersecting the specimen axis, although during any unequal elongation the up- 60 per and lower" heads will assume a slightly inclined position which is permitted due to the relieved portions I3 while further flexibility of the two heads is permitted by the relieved portion 6. T0 in'sure that the abutment points 33 and 33 will both remain in complete contaot with the separable head during any inclination of the upper and lower gripping heads, the strain followup springs 22 and 23 are disposed preferably in alignment with each 015 the abutment points 33 70 and 34.

obtainecl the average elongation of the speclmen' From the foregoing disclosure lt is seen that I- data to be obtained right u p to the point o! tailure. It Is also seen that I ha ve provided in an instrument cf thls kind an extremely rugged construction and yet one whlch lras all the sensitivity and reflnements rlaqu.ired in a scientitlminstrument o1 this character together with simple and eflectlve means for obtaining the average v stra'.in together with other features hereinbetore set torth or which are inherent in the structure disclosed including, tor instance, the adaptability ofthe Instrument for compression or tension lo'ading o'r tot loadlng 8.l'ld unloading under eit.her tension er compression teste thereby to obtal n 'hysteresis data.

It will of course be undrrstood the/t those skilled in the art may obtain the various results and advantages o1,- my invention by making varlous each other when the extensometer is attached to a spt'ecimen normally inactive means operative upon failure of a Specimen to limit movemei1t 013 said frame, and strain responsive means operatively associated with said Irame.

2. An extensometer comprising a. main frame formed of inflexible relatively'flat thin material with relieved flexible portions, the thin edges of said Irame lying in planes substantially parallel to the axis of a specimen to be tested, a gripping head carried by said frame and otlset thereirom both axially and transversely 01 the specimen. gauge points carried by said head for attaching said frame to a. specimen. a dummy he ad also carried by said frame, a substantially U-shaped separable gripping hearl, abutment points through whl ch said separable head is normally supported on said dummy head in spaced relation thereto. and gauge points carried by said separable head for engaging a. specimen.

3. An extensometer comprising a main frame 'formed of inflexible relative'ly flat thin material with relieved flexible portlons, the thin edges of said frame lying in planes substantially parallel to the axis of a specimen to be tested, a gripp'lng head carrlecl by said frame and ofiset therefrom both axially and transversely o1 the specimen, gauge points carried by said head for attaching said frame to a specimen, a dummy head also carried by said Irame, a substantially U-shaped separable gripping head normally disposed in supportlng contact with said dummy head. and gauge points each adjustably carried by said separable head for engaging a specimen.

4. An extensometer comprising an integral U- shap:zflexible frame, a gripping head formed an one end 01 the frame for direct attachment to a specimen, a dummy head formed on the other end of the frame, a second gripping head for direct attachment to a specimen and 'adapted during such attachment to have a normally flxed contact with said dummy head but being adapted to separate thereirom upon failure of the specimen, and strain indicating mechanism associated with the two ends o! the integral U-irame. 5. An extensometer comprising an integral U- shape flexible frame, a gripping head Iormed on one end o! the frame tot direct attachment to a speclmen. a dummy heacl formed on the other end of the trame. a. second gr:lpplng head 1or direct attachment to a specimen und adapted during such attachment to have a normally flxed 5 cdntact with saicl dummy headbut belng adapted to separate therefrom upon fallure 013 the spec1- man. mea.ns between the dummy head und second gripping head to maintaln the same in normally flxed lateral relation, am! straln lndicatingmech- 10 anlsm associated w1th the two ends cf the integral Uframe. v

6. An extensometer comprlslng an integral U- shape flexible Irame, a gripplng head Io rmed on one end 01 the fra.me 10r direct attachment to a m specimen, a dummy head formed on the other end o1 the frame, a. second gripping head for dlrect sittachment 1:0 a speclmen and adapted durlng such atta.chment to have a normally flxed contact w1th sald dummy head but being adapted'to separate 20 theretrom upon fallure cf the specimen, and strain indlcatlng mechanlsm assoclated wlth the two arate therefrom upon fallure otthe specimen,

sprlngs tor urglng said first' gripplng head end said dummy hea'd away Irom each other thereby to malntaln sald normally flxed contact wlth the second grlpping hea.d and stra.in indlcatlng mechanlsm associated yvith the two ends of the integral U-1rame.

GERD S. VON HEYDEKAMPF'. 

